Seeding the second stars: enrichment from the first stars, dust evolution and cloud collapse
speaker: Gen Chiaki
Abstract:
I have investigated the process of chemical enrichment and evolution of stellar mass in the first billion years after the Big Bang. The first-generation of stars (Pop III stars) are born in chemically pristine, metal-free gas clouds. For the lack of cooling efficiency, the clouds collapse stably against fragmentation. Then, Pop III stars are believed to be massive (~100 Msun). After Pop III stars die with supernova (SN) explosions, metals and grains are dispersed to the interstellar medium. In clouds enriched with metals, the second-generation, metal-poor stars (Pop II stars) form. Due to additional cooling efficiency mainly from grains, the enriched clouds become unstable to fragment. Then, the first low-mass stars (~1 Msun) can form as metal-poor stars. The process of metal enrichment from Pop III stars is poorly known, because the distribution of ejecta is highly complex. Also, we do not have sufficient knowledge of the condition for cloud fragmentation. In this study, we carry out cosmological three-dimensional simulations from Pop III star to Pop II star formation, following the metal enrichment process. We find that Pop III SNe enrich the halos that host the Pop III stars. This indicates that the self-enrichment of the host halos is the main channel of metal enrichment from Pop III SNe. We also find that several enriched clouds fragment into low-mass clumps due to dust cooling. Since low-mass stars can survive for the Hubble time, the simulated low-mass Pop II stars can be observed in the present day as metal-poor stars in our vicinity.